Spatio-Temporal Distribution of Actual Evapotranspiration in Jhelum and Chenab Canal Irrigation System

Abstract

During the past few decades, fast increasing world population along with urbanization and industrialization has resulted in depletion of fresh water resources. In Pakistan agriculture plays a fundamental role in national economy which is mainly dependent on irrigated agriculture. Thus this sector is the main consumer of water. Evapotranspiration (ET) is key component of water cycle and its estimation in water scarce country like Pakistan plays an important role in water resources monitoring and management of irrigation discharge. The increase in water demand, due to population growth and economic development can affect the long-term water supply. The estimation of water consumption is also vital for distribution of water, the crop water requirement and enlargement of storage reservoirs. Several ground and remote sensing methods have been developed for estimation of evapotranspiration at various spatial and temporal scales. The ground based methods provide point measurements, the process is very hectic, time consuming and expensive and can only represent a small area compared to remotely sensed methods. The satellite remote sensing provides an opportunity for the estimation of Evapotranspiration over large areas. In present study ET is estimated in canal command areas of Jhelum and Chenab and the total area is 6.5 million acres. The Surface Energy Balance System (SEBS) model has been used for estimation of Evapotranspiration using moderate-resolution imaging Spectroradiometer (MODIS) data and Meteorological data obtained from Pakistan Meteorological Department. A large variation in Seasonal evapotranspiration has been observed. The ET values start increasing from March and the maximum values have been observed during the pre-monsoon season around 6.1 mm. This season starts from mid-April to June with hot short nights, long intense days with Peak temperature. The Evapotranspiration values have gradually decreased over the months and the lowest values have been observed in the winter season mainly in the month of January around 1.1 mm. The reason is the drop in the temperature along with the low soil moisture due to low precipitation in winter season. The surface energy balance algorithm (SEBS) is capable of estimating Evapotranspiration fairly well (R2 0.87) as compared to the Reference ETo obtained from Pakistan Meteorological department at Regional Agro-Met station. The Results show that the remotely sensed datasets are useful for tracking changes in Evapotranspiration over large areas and with high temporal frequency. Among the various Meteorological variables, temperature followed by wind & sunshine significantly (P<0.05) impacted the evapotranspiration values, xiv whereas relative humidity has shown a negative trend. The variation in Evapotranspiration directly impacts the crop water requirement and these Evapotranspiration maps can help the water resource managers in monitoring water use and can help in irrigation management. A proper water management policy is mandatory in Pakistan to avoid severe water shortage in the near future. There is a need to drive precision agricultural technologies in Pakistan along with high efficiency Drip Irrigation techniques. These techniques will help the policy-makers in planning effective irrigation measures towards the sustainable development in Pakistan.